"It's a nasty situation," said Susan Haig, a wildlife ecologist at the U.S. Geological Survey in Corvallis, Ore. The spotted and sparred owls are hard to tell apart, and hybrids are not protected under the Endangered Species Act. "This could cause the extinction of the Northern spotted owl," she said.

Like an increasing number of creatures around the world, the barred owl may interbreed itself out of existenceand scientists and government agencies are taking notice.

When unrelated species meet and mate in the wild, it can create an ecological nightmareespecially if it involves endangered animals. When populations dip so low that every baby that's bornor hatchedcounts, interbreeding can further limit reproductive success.

Some hybrids are born sterile, but that doesn't mean they don't cause other problems, explains Judith Rhymer, a conservation geneticist at the University of Maine. "It's still a conservation issue because parents are contributing less and less to the next generation," she said.

Although hybridization is a natural evolutionary process, "problems arise when it's human-caused," said Nina Fascione, vice president of species conservation for the Defenders of Wildlife.

Human Introductions

And that's the crux of the problem. Humans are bringing together animals that have never seen each other before, either through habitat destruction, the international pet tradeor travel.

The owls are just such an example. "Barred owls may be invading because there's been so much deforestation from logging," Haig explains. Logging creates the more open environment that the newcomers prefer, and the owls continue to move as forests are leveled.

The endangered red wolf is another case in point. Hunting and habitat loss slowly decimated wolf populations until they finally went extinct in the wild in the 1980s.